This invention relates generally to the field of fuel nozzles and, more particularly, to a single-mode flame holding, tip-cooled combustion engine fuel nozzle.
Combustion engines are machines that convert chemical energy stored in fuel into mechanical energy useful for generating electricity, producing thrust, or otherwise doing work. These engines typically include several cooperative sections that contribute in some way to this energy conversion process. In gas turbine engines, air discharged from a compressor section and fuel introduced from a fuel supply are mixed together and burned in a combustion section. The products of combustion are harnessed and directed through a turbine section, where they expand and turn a central rotor. The rotor produces shaft horsepower or torque; this output shaft may, in turn, be linked to devices such as an electric generator to produce electricity.
As the need for electricity rises, so to do the performance demands made upon industrial turbine combustion engines. Increasingly, these engines are expected to operate at increased levels of efficiency, while producing only minimal amounts of unwanted emissions. Various approaches have been undertaken to help achieve these results.
One approach has been to utilize multiple single-mode nozzles arranged in discrete groups to form a so-called xe2x80x9cdry, low-NOxxe2x80x9d (DLN) combustor. DLN combustors typically provide lowered amounts of unwanted emissions by lowering the burning temperature and by premixing the fuel and air and by providing independent flows of fuel to two or more discrete groups or xe2x80x9cstagesxe2x80x9d of nozzles, with each stage contributing in a different manner to the overall combustion process. Two common gaseous fuel stages found in DLN arrangements are the xe2x80x9cpilotxe2x80x9d and xe2x80x9cmainxe2x80x9d stages. Quite often, the pilot stage is a fuel-rich xe2x80x9cdiffusionxe2x80x9d nozzle capable of holding a flame. Diffusion-type nozzles are quite stable, but they unfortunately provide a source of combustion hot spots that lead to the formation of NOx emissions. To keep these unwanted emissions at a minimum, typically only one diffusion nozzle is used in a given combustor. The main stage nozzles, therefore, typically operate in a xe2x80x9cpremixxe2x80x9d mode, producing a mixture of fuel and air that burns through interaction with other flames, such as the fuel-rich flame produced by the pilot stage. Although this arrangement produces relatively-low levels of NOx emissions when compared to diffusion-only combustors, the presence of only one flame-holding nozzle reduces operational flexibility. This limitation, combined with the NOx emissions produced by the pilot nozzle diffusion flame, make traditional DLN combustors unsuitable for many settings.
In an attempt to reduce NOx emissions even further and to provide increased operational flexibility, combustors that employ flame-holding nozzles capable of operating in a premix mode have been developed. Typically, these combustors employ at least one pilot nozzle capable of providing a diffusion flame to initiate startup combustion. Multiple flame-stable nozzles capable of operating in a premix mode are included to support combustion during the majority of remaining operating conditions. While the use of flame-holding premix nozzles advantageously reduces NOx emissions levels and may provide increased operational flexibility, efforts to produce such a nozzle have met with difficulty. This type of nozzle must not only produce a controlled stream of mixed fuel and air, it must also provide tip cooling to avoid melting as combustion temperatures rise to meet increased demands for power output. Flame-holding diffusion nozzles also face tip cooling and fuel dispersion requirements and present similar difficulties. Nozzles attempting to provide these characteristics have succeeded to varying degrees. For a variety of reasons, however, the practical difficulties imposed by meeting these requirements simultaneously has resulted in nozzles that are prone to leaks, are not reliable, and which may actually reduce efficiency due to losses generated by a large number of components.
Accordingly, there exists a need for a flame-stable nozzle that provides tip cooling and controlled fuel dispersion in a simplified manner. The nozzle should transmit cooling air in a passive manner through a dedicated passage that eliminates the need for complex valve arrangements, thereby reducing costs and increasing reliability. The nozzle should also include discrete fluid-guiding regions that are sealed in a leak-resistant manner without the reliance upon bellows or slip fits.
The instant invention is a single-mode, flame-holding nozzle for a gas turbine combustion engine that provides passive tip cooling and controlled fuel dispersion. The nozzle includes several elongated sleeves that cooperatively form discrete passageways adapted to transmit fluids through the nozzle. The nozzle includes conduits that allow fuel and cooling air to reach designated fuel and cooling passageways without mixing. This arrangement advantageously ensures that air used to cool the nozzle does not become flammable, thereby reducing the chances of unwanted flashback occurrences. Portions of the nozzle sleeves are also strategically arranged to transmit fluids in a manner that provides substantially-uniform thermal expansion, thereby reducing the need for sliding joints or bellows arrangements.
Accordingly, it is an object of the present invention to provide a single-mode combustor nozzle having tip cooling and controlled flame-holding capabilities.
It is another object of the present invention to provide a single-mode combustor nozzle that includes a dedicated cooling fluid passageway that eliminates the need for complex valve and manifold arrangements.
It is another object of the present invention to provide a single-mode combustor nozzle that includes discrete fluid-guiding regions that are sealed without the need for sliding joints or bellows arrangements.